Chriske

I'll tell you all about when finished and assembled. Should be very soon...;-) Planning to use it on my equat. platform. Observing visually will not be a problem, nor taking pictures with a widefield lens on a tripod on top of that platform.

Busy printing this one this very moment... Its a three stage drive. The holes on which the 'planets' rotate, I'll fill them with brass rods instead of printed versions. I also will redraw the part on the right, to allow a stepper instead of a round DC motor. The outer diameter of that thing is about 95mm, small enough for me.

Thanks Stu, picture just sent..👍

Nice, very nice indeed...! Going to make me one, a strain wave gear...👍

It's not a good idea to give different opinions while searching for solutions in a case like this. It's most confusing for kbrown. So Nigel please you continue helping to solve this problem. To be clear : no hard feelings here.

And one more thing. Maybe you already removed the alu sheet. If not, While cutting, leave the silicone blobs on the SM.

Before you re-glue the mirror to that sheet of alu, do one more test please.

Remove that sheet of alu. You can now continue without that heating system. If you hold on to that heater you need to soften the aluminium to get rid of that strain. I'll explain later how, it is not the same as softening metal...!! The silicone blobs should be much smaller and very near the edge, almost peeking out of the perimeter of that SM.

Oops ...! looking bad that heating system. How hot does that thing get...? (about)

Carefully place the flat agianst the SM and see what result you got. See that there are no dust particles between SM and reference flat...! do not remove the alu-sheet at this point. take a picture of that result. Next remove that aul-sheet, and do exactly the same. Compare these two pictures and post them both here please. This way you can eliminate possible problems of that alu-sheet.

Ok, some issues can be eliminated after that last post. You need to concentrate on that SM or it"s holder. a few possibilities there. Before we go to removing strain out of that sheet of alu...this is most important not to do that yet. You need to rule out some possibilities first. - Do you have a reference flat..? -Do you have a Foucaulttestes and know to use it..?

If the backing plate is warping then it should not distort the shape of the mirror, as you said Nigel. That is correct. But what about the size of the blobs..? I'm afraid (tell me If Im wrong here kbrown) that the blobs are not to big. That's why I asked before to make an estimate drawing about that. Heating a mirror, be it Pyrex, Duran or any other decent glass it should not deform at all, by the heating it that is. That's what all these types of glass are suppose to do, hold its shape when cooled or heated. And btw 1 or 2 degrees should not warp any mirror at all. Let's first find out what kbrown has to say about the quality of his mirrors. First : Make a picture, same as above, turn he primary mirror 90° around it's optical axis in it's holder and make a second picture holding the same position of camera and scope. What happened with the pattern.? Did it hold it's position or not...?

The very first error has nothing to do with this new astigmatic pattern, as you can see. Twee different causes.

You need to adjust the heat to just one, or two degrees above ambient. Just enough to keep the dew away from that SM. But as your SM has already astig, when cold, there's another problem. Looking at the surface of the aluminium I think that sheet of alu is most probably hardened alu. Meaning that sheet of alu is full of strain. That has to be removed first. Now as it is heating that sheet of alu the tension in the alu get worse and pulls on that mirror. You need to remove that strain by softening the alu. Sadly enough you need to remove the mirror first from that sheet of aluminium. If you do not know how let me know. BUT what I do not understand is why the ast has a perfectly elliptical shape. Maybe just maybe it has nothing to do with that hardened sheet of alu. at all. First this : Are you ab-so-lu-tel-y sure that both these mirrors are free of astigmatism...!!! Maybe in the past you didn't notice..? Can the primary mirror move freely in it's holder. Just a fraction of a millimetre is enough. The clamps/hooks (to hold the mirror down), are they not to tight. Make drawing please, were are the silicone blobs located..? It's not a major issue, but it could reinforce the error you're dealing with right now.

Hold on, you're saying(if I understand it correctly) : no heating and there's practically no astigmatic error at all .. ?

Al done. Also adapter for another scope(blue)

Stu, Can I please use one or two of your pictures to show on a Dutch forum. There are a few non-believers here about pictures taken with a smartphone. That'll convince them that it actually can be done. Yours are far better then mine, but I think that will change in time. I hope to reach the same level as yours and that of others here on this forum. It's almost mind boggling what can be done with these small lenses in a smartphone. I fact it tells something about the quality of these little lenses...😳 Chris

I'm drooling all over the place....😱

Of course....! ... Why didn't I think of it myself, silly me... I thought only the FL would change position of the SP.

Btw...estimate cost for this printed holder is 6.5€ + a few nuts and bolts M3

Thanks...!...👍

Hey Stu, thanks for the reply. I can shift the SP 20mm sideways in both directions. The third movement (optical axis direction) planning to adjust even further. Depending on the F value of the eyepiece I think that needs to go even further(or nearer) But the latter is just a guess, not done this before at all. I'm jumping in a dark and deep hole here. Love it to do this project together with my son Steven...🤗 Anyway I'll keep you informed about our progress. Problem is now...it doesn't look good for the next days ....it's cloudy again...😟

Well, as a matter of fact, it crossed my mind. But owning a few printers I'd rather make my own. That's (to me that is) part of the fun.! this is what I've got so far... Almost done. I can adjust the SP in three directions with this holder. Busy printing the first part already. The longer part on the left fits around the focusserbarrel, 70mm diameter that is.

The picture above is taken handheld as I mentioned before. It is very hard to get the SP perfectly aligned with the scope's optical path. The SP holder I used before(see higher up) is not perfect. It is off by (not even) 1mm. So I will make me another holder. I intend to make it so that all three directions can be corrected if needed. Never gave it a thought that it should be so precise. Has someone else had that same problem...?

Yep, I am very proud indeed. Time to move on to our next challenge. It will be even bigger...!